The mechanism of regulation of immunoglobulin heavy chain class switching remains unknown. Recent work from the laboratory of Dr. Fred Alt revealed the importance of sequences found 3' of the mouse heavy chain locus. B cells with a neomycin resistance gene replacing the 3' IgH enhancer were generated, and found to display an altered regulation in immunoglobulin isotype switching. The finding of this major regulatory element of IgH constant region genes may provide a key for understanding physiologic and pathologic aspects of immunoglobulin production. We propose to generate mice with a targeted germline deletion of the 3' IgH enhancer. This would create a model to study how this 5kb element exerts control over a l20kb portion of the IgH locus, addressing fundamental questions about how tissue specific gene expression is maintained, and subsequently changed during differentiation. The role of B cell activation signals and cytokines on IgH class switching, as well as mechanisms influencing IgH gene somatic hypermutation will be studied with this model. Importantly, these topics are directly relevant to human diseases such as the Ig deficiencies, immediate type hypersensitivities, and lymphomas involving translocations with c-myc. In the first phase of this proposal, the candidate will focus on learning the theory, approaches, and techniques used in current molecular biology. Phase 2 will focus on applying these techniques to make significant contributions in the understanding of B cell differentiation. The overall objective of this proposal is twofold; first to offer the candidate an intense training in molecular and cellular biology in preparation for an independent research position. Secondly, to provide important, clinically relevant insights in molecular immunology.